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Understanding CH-Stretching Raman Optical Activity in Ala-Ala Dipeptides
Marius Hope1,2, Jaroslav Šebestík1, Josef Kapitán3
1Institute of Organic Chemistry and Biochemistry , Academy of Sciences , Flemingovo náměstí 2 , 16610 Prague , Czech Republic.
The Journal of Physical Chemistry. A
|January 7, 2020
Summary
Raman optical activity (ROA) can now reveal peptide structure in the challenging CH-stretching region. Complex simulations are needed to interpret this rich structural information from peptide CH-stretching ROA signals.
Area of Science:
- Spectroscopy
- Computational Chemistry
- Biophysics
Background:
- Raman optical activity (ROA) is a standard technique for monitoring peptide conformation.
- The CH-stretching region in ROA spectra is difficult to measure and interpret.
- Understanding this spectral region is crucial for detailed structural analysis of peptides.
Purpose of the Study:
- To investigate the structural information contained within the CH-stretching region of ROA spectra.
- To analyze ROA data of the model Ala-Ala molecule using experimental and computational methods.
- To understand the origin of ROA signals in the CH-stretching region and their relation to molecular conformation.
Main Methods:
- Acquisition of ROA spectra for Ala-Ala enantiomers using a custom-made spectrometer.
- Analysis of experimental ROA data aided by molecular dynamics (MD) and density functional theory (DFT) computations.
- Application of second-order perturbation and vibrational configuration interaction for anharmonic corrections.
Main Results:
- Reliable measurement of ROA signals in the CH-stretching region was demonstrated, despite a low ROA/Raman intensity ratio.
- Theoretical modeling attributed intense ROA bands to locally asymmetric CH3 and αCH vibrations.
- Anharmonic corrections were necessary for accurate spectral feature assignment, including combination and overtone vibrations.
Conclusions:
- The peptide CH-stretching ROA signal contains extensive structural information, including environmental effects.
- Complex spectral simulations are required to fully decipher the experimental ROA data in this region.
- ROA spectroscopy, when combined with advanced computational methods, offers a powerful tool for peptide structure elucidation.
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